Rotary die heads having a plurality of circumferentially spaced, radially movable cutting tools are well known in the art. Reference may be had for example to U.S. Pat. Nos. 3,082,446; 3,645,638 and 3,812,548. These rotary die heads cut threads of uniform and continuous groove configuration in the workpiece in one pass.
However, a thread joint for oil well tubing has recently been developed having a tapered thread configuration with the pitch diameter and crest or pitch width increasing from one thread end to the other. Reference may be had to U.S. Pat. No. 3,989,284 for a showing of such a threaded connection. In this thread configuration, the load flank and stab flank are at different leads. This type of connection will be referred to hereafter as a dual lead tapered thread. This type of thread is not believed to be in commercial production but is expected to be used in applications where the integrity of the threaded connection is important.
In trying to make the dual lead tapered thread in conventional rotary die head operations, at least two passes have been required because of the different flank leads and increasing pitch diameter and crest width. The necessity for having more than one pass of the workpiece with currently available rotary die heads will increase production time and expense.